For example, underpants-type disposable diapers are each provided with an outer member including a front body and a back body and an inner member including an absorber fixed to the inner face of the outer member, the front body and the back body of the outer member being bonded at two opposite side edges to define a waist opening and right and left leg openings. In an underpants-type disposable diaper, elongated resilient and elastic members, such as rubber threads, are stretched and fixed to various portions of the outer member in the circumferential direction to provide a stretchable structure in the direction around the waist for enhancement of the fit to the body. Some underpants-type disposable diapers provided with waist-edge resilient and elastic members along the edge of the waist opening in the width direction and under-waist resilient and elastic members along the width direction closer to the crotch portion than the waist-edge resilient and elastic members have a relatively tight fit to the body and are commonly used.
In contrast, typical tape-type disposable diapers have the following structure: tape-type disposable diapers each includes a crotch portion, a ventral portion extending to the front side of the crotch portion, a dorsal portion extending to the back side of the crotch portion, an absorber provided in an area including the crotch portion, fastening tapes protruding from both sides of the dorsal portion, and target tapes disposed on the external face of the ventral portion and attachable to the fastening tapes; and the fastening tapes extend from both sides of the waist to the external face of the ventral portion and are attachable to the target tapes, to fix the diaper to the body. Such tape-type disposable diapers are commonly used for babies and toddlers and for nursing care (adults). In general, the fit of tape-type disposable diapers around the waist is lower than that of underpants-type disposable diapers. This is improved by stretching and fixing elongated resilient and elastic members, such as rubber threads, to the dorsal portion and the fastening tapes along the width direction, to provide a stretchable structure in the direction around the waist.
An improved stretchable structure, as illustrated in FIG. 17, is proposed (refer to PTL 1) in which multiple sheet bonding sections 20 are formed by intermittently bonding together two sheet layers 12H and 12S in the stretchable direction and the direction orthogonal to the stretchable direction; disposing multiple elongated resilient and elastic members 19 between the two sheet layers 12H and 12S without passing through the sheet bonding sections 20 (so as to pass through non-bonding sections); and fixing only the ends of each resilient and elastic member 19 to the sheet layers 12H and 12S. In the stretchable structure according to the traditional art, the sheet bonding sections 20 aligned in the longitudinal direction define grooves extending in the longitudinal direction, and two sheet layers protrude in opposite directions (from the front and back faces) by approximately the same height to define corrugations 80 in areas between the grooves, to provide a bellows structure as a whole. The corrugations 80 expand in the stretchable direction in a moderately stretched state, whereas the corrugations, which are thin in the stretchable direction, are continuously aligned in directions orthogonal to the stretchable direction, the material for the corrugations is folded over with a small radius of curvature at the tops of the corrugations to form creases, and the corrugations having such creases are aligned at the same height and close to each other in an unstretched state. The sheet bonding sections 20 illustrated in FIG. 17 are to be formed through welding of the sheet layers 12H and 12S. Alternatively, the sheet bonding sections 20 may be formed through the use of an adhesive, to define corrugations 80 having the same shape.